Debugging and Testing

Compare ticket_price with ticket_prce letter by letter. A NameError often reveals an inconsistent spelling.

One possible implementation. Check the book's tests and try an extension after comparing.

# Challenge 61 - The Missing Variable
# Use one spelling for each variable name.
ticket_price = 12
booking_fee = 3
total = ticket_price + booking_fee
print(f"Total: {total}")

The return after if must be indented under if; the return under else must be indented under else.

One possible implementation. Check the book's tests and try an extension after comparing.

# Challenge 62 - The Indentation Trap
def eligibility(age):
    if age >= 16:
        return "Eligible"
    else:
        return "Not yet eligible"

age = int(input("Enter age: "))
print(eligibility(age))

input() always gives text. Use float() on each input before adding; format with :.2f when printing.

One possible implementation. Check the book's tests and try an extension after comparing.

# Challenge 63 - The Price That Became Text
first = float(input("First price: "))
second = float(input("Second price: "))
total = first + second
print(f"Total: {total:.2f}")

range() excludes its stop value. For N inclusive turns, use range(1, N + 1), not N + 2.

One possible implementation. Check the book's tests and try an extension after comparing.

# Challenge 64 - One Extra Turn
def show_turns(turns):
    if turns < 1:
        return []
    return list(range(1, turns + 1))

turns = int(input("How many turns? "))
for turn in show_turns(turns):
    print(f"Turn {turn}")

The condition should cause repetition only when the entered value is invalid. A while True loop with break is one simple fix. Stop the faulty starter with Ctrl+C if it keeps asking.

One possible implementation. Check the book's tests and try an extension after comparing.

# Challenge 65 - Validation That Never Ends
def valid_score(value):
    return 0 <= value <= 100

while True:
    score = int(input("Enter score (0-100): "))
    if valid_score(score):
        break
    print("Out of range. Try again.")
print(f"Accepted: {score}")

Call strip() first, then test if the result is empty before attempting [0].

One possible implementation. Check the book's tests and try an extension after comparing.

# Challenge 66 - The Empty String Crash
def first_initial(text):
    name = text.strip()
    if not name:
        return "No initial"
    return name[0].upper()

name = input("Enter a name: ")
print(f"Initial: {first_initial(name)}")

Filter to numbers before calling sum() and len(). If none remain, return None instead of dividing.

One possible implementation. Check the book's tests and try an extension after comparing.

# Challenge 67 - No Items in the List
def average_numeric(values):
    numbers = [v for v in values if isinstance(v, (int, float)) and not isinstance(v, bool)]
    if not numbers:
        return None
    return sum(numbers) / len(numbers)

for scores in ([10, 20, "absent", 30], [], [0]):
    result = average_numeric(scores)
    print("No numeric scores." if result is None else f"Average: {result:.2f}")

Count how many values are present, not how many gaps are between them. Be sure the single-item test does not divide by zero.

One possible implementation. Check the book's tests and try an extension after comparing.

# Challenge 68 - The Incorrect Average
def average(scores):
    if not scores:
        return None
    return sum(scores) / len(scores)

for scores in ([10, 20, 30], [5], [2, 4, 6, 8]):
    result = average(scores)
    print(f"Average: {result:.2f}" if result is not None else "No scores.")

Use return number * 3, not print(). A good test stores or compares the returned result.

One possible implementation. Check the book's tests and try an extension after comparing.

# Challenge 69 - Where Did the Answer Go?
def triple(number):
    return number * 3

def check_cases(cases):
    passed = 0
    for value, expected in cases:
        actual = triple(value)
        if actual == expected:
            passed += 1
        else:
            print(f"FAIL {value}: expected {expected}, got {actual}")
    print(f"Passed: {passed}/{len(cases)}")
    return passed

cases = [(0, 0), (1, 3), (2, 6), (-2, -6), (4, 12)]
check_cases(cases)

Loop over (name, expected, actual). Compare values, count mismatches and include all details in each FAIL message.

One possible implementation. Check the book's tests and try an extension after comparing.

# Challenge 70 - The Three-Fault Challenge
def faulty_double(n):
    return n + 2  # Wrong for most inputs

def faulty_initial(text):
    return text[0].upper()  # Does not remove leading spaces

def faulty_total(items):
    return items[0]  # Ignores the remaining item prices

def report_results(cases):
    failures = 0
    for name, expected, actual in cases:
        if expected == actual:
            print(f"PASS {name}")
        else:
            failures += 1
            print(f"FAIL {name}: expected {expected!r}, actual {actual!r}")
    print(f"Failures: {failures}/{len(cases)}")
    return failures

cases = [
    ("doubling", 8, faulty_double(4)),
    ("first initial", "A", faulty_initial("  Alex")),
    ("total cost", 9, faulty_total([4, 5])),
    ("sanity check", 2, 1 + 1),
]
report_results(cases)